DESCRIPTION: Axons contain an elaborate cytoskeleton that consists of microtubules, neurofilaments, and microfilaments. The cytoskeleton comprises an architectural framework that defines the external shape of the axon and also organizes the intracellular motility necessary to grow and maintain the axon. Thus the mechanisms that establish the cytoskeleton in neurons contribute directly to the elaboration and maintenance of neuronal form and thereby function. This application proposes direct experiments on the dynamic processes that generate the cytoskeleton in growing axons. These experiments focus on the class of microtubule proteins known as microtubule-associated proteins (MAPs). MAPs promote the assembly and stabilization of microtubules in vitro, and also integrate microtubules with other cytoskeletal elements. The goal of the proposed experiments is to define the functional specializations of MAPs in axon growth. The applicant hypothesizes that MAPs coordinate the assembly and stabilization of microtubules with the motile events that underlie the initiation and continued growth of the axon. To test this hypothesis, he has developed a novel approach for evaluating the functional specialization of MAPs in axonal growth with involves microinjection of anti-MAP antibodies into cultured neurons to selectively inactivate specific MAPs. The consequences of MAP inactivation on axonal growth and axonal microtubules are then evaluated. The proposed experiments combine microinjection of anti-MAP antibodies into cultured neurons with high resolution video and fluorescence microscopy to evaluate the effects of MAP inactivation on axon structure, growth cone motility, and the organization, assembly dynamics and stability of neuronal microtubules. He has already used these approaches to demonstrate that MAP1b, a major MAP in growing axons, is apparently essential for the initiation and continued elongation of axons in culture, Successful completion of the proposed experiments will define essential mechanisms involved in generating the microtubule arrangements required for the normal growth of axons. In addition, many pathologies of the nervous system are characterized by abnormalities of cytoskeletal organization. By defining normal mechanisms for generating and maintaining microtubule arrangements in neurons, the proposed research will contribute toward a better understanding of these pathologies.